CH301H - Principles of Chemistry I: Honors
Fall 2015, Unique 49310

Lecture Summary, 15 October 2015

Multi-electron Atoms:  The Schrodinger equation cannot be solved exactly for any atom with more than one electron.  It can, however, be approximated using several different techniques, and it has been shown to produce accurate predictions of experimental observations.  We will therefore use the atomic orbitals that we built up for our hydrogen atom for multi-electron systems. We combined the Pauli exclusion principle and Hund's rule into the Aufbau ("building up") rules.

Pauli Exclusion Principle: No two electrons in the same system (in this case a single atom) can share the same set of quantum numbers.  Violations are NOT allowed.

Hund's Rule: When putting electrons into degenerate orbitals, put an electron into an empty degenerate orbital with the same spin as other degenerate orbitals until the degenerate set is half filled.  Then beginning pairing electrons of opposite spin in the same orbital.  Violations are allowed, but result in a higher energy (i.e. not the lowest energy or "ground") state.

Atomic Orbitals and the Periodic Table:  We spent some time revisiting our old friends the periodic trends.  We found that we can now explain these trends completely in terms of the available atomic orbitals for each electron, and no longer have to resort to the squishy and hand-wavey explanations.  In fact, if we started from the AO's, we would have been able to predict the experimentally observed periodic trends knowing nothing about the experimental data.